[Zipperfish]

BartSimpson BartSimpson:

Zipperfish Zipperfish:

2. Don't get this one at all.

Simple: It's proposed that CO2 causes the climate to warm. Great. Then by what mechanism does an ice age start to cause the decline of a CO2 induced warm period?

Logically, the presence of high levels of CO2 should preclude any such cooling, yet the record shows that exactly that has happened. Despite high CO2 levels the climate has cooled down to an ice age.

Really, this is the heart of the AGW question is to not only say what causes warming but to define what causes cooling. Because if you define what causes cooling then you are on track to proving (or disproving) that a warming cycle is evident.

It's not proposed that CO2 will cause the climate to warm--and it's pretty much incontrovertible. The uncertainty arises around how the ecosystem responds. For instance, the oceans may absorb more CO2 to maintain the equilibrium, or there will be more cloud cover, etc. It's what's known as climate sensitivity in the scientific jargon. A climate sensitivity greater than one means the effects of CO2 are amplified by the Earth's ecosystem (it's warmer than the physics would indicate) and a climate sensitivity less than zero indicates CO2 effects are attenuated (it's cooler).

There are, of course, several other factors that influence global temperature. By far the most important is the sun--so we have the eleven year sunspot cycle, the 21,000 year tilt cycle. the 41,000 year wobble cycle and the 100,000 year cycle for changes in the Earth's elliptical orbit. Large changes in solar variability would have a much more significant effect than CO2. Though I suppose you would expect that, if solar variability caused a drop in temperature, you would also see a drop in CO2 concentration.

Another possibility is that the data showing simultaneous very high CO2 concentrations and an ice age are incorrect--not beyond the realm of possibility given that we're dealing with a time span of 500 million years. Given that mnay climate change skeptics point out errors from the temperature record just over the last 150 years, it's easy to accept that data from a half-billion year time span could be off a bit. Even a 1% error in time would be 5 million years.